In recent years, a car often includes a switch fixed at a car body side of a door section so as to detect the opening/closing of a door. A signal detected by the switch is used for turning ON or OFF the room light, locking or unlocking doors, or the like. Such a detecting switch is also used for controlling highly advanced security systems, for example, known as the keyless entry system. Here will be described a conventional switch for a vehicle with reference to FIGS. 7 and 8.
FIG. 7 is a sectional view of a conventional switch for a vehicle (hereinafter, referred to as a vehicle switch), and FIG. 8 is an exploded perspective view of the vehicle switch. Insulating resin case 21 has a box-like structure in which the top surface is open. Operation component 22 includes generally cylindrical-shaped operation head 22A in the upper section. Operation component 22 is housed in case 21 so as to be movable in the vertical direction. Substrate 23 is made of insulating resin and formed into a flat plate. On both surfaces of substrate 23, a plurality of wiring patterns (not shown) are formed and then a resistance element and other electronic components are mounted thereon. In addition, on the right surface of substrate 23 as seen in FIG. 7, fixed contacts 24A and 24B made of metal are oppositely disposed so as to be substantially parallel to the moving direction of operation component 22.
Fixed contacts 24A and 24B are connected via the wiring patterns to a plurality of terminals 25, and terminals 25 are fixed in the lower section of substrate 23. Substrate 23 is accommodated in case 21, with the bottom end being held by holder 26. Movable piece 27 is made of a metallic thin plate and is substantially U-shaped. The bottom and one arm of the “U” are held by the bottom section of operation component 22. The other arm of the “U” has contact hooks 27A and 27B at the lower end. Contact hooks 27A and 27B make contact with fixed contacts 24A and 24B, respectively.
Coil spring 28 is assembled between the inner bottom of case 21 and the bottom of operation component 22 under a slight initial compression to urge component 22 upwardly. Mounting plate 29 is made of a steel plate. Case 21 is fixed to the left side of mounting plate 29, and on the right side of plate 29, mounting hole 29A is disposed. Waterproof cover 30, which is made of rubber, thermoplastic elastomer, or the like, covers the upper surfaces of operation head 22A and mounting plate 29.
In the actual use of the vehicle switch structured as described above, terminals 25 protruding from the bottom of case 21 are connected to an electronic circuit (not shown) of a car. The switch is attached to a part of the chassis (not shown) facing an end of a door (not shown) by a screw (not shown) through mounting hole 29A.
Now will be described the workings of the vehicle switch. Contact hooks 27A and 27B, as shown in FIG. 7, make contact with fixed contacts 24A and 24B, respectively. While the electrical connection is maintained (i.e., during the ON-state), fixed contacts 24A and 24B carry, for example, a current of 1-10 mA at 12 volts d. c. via movable piece 27. When the door confronting the switch is closed, the edge of the closed door pushes operation head 22A covered with waterproof cover 30. Operation component 22 moves downwardly and compresses coil spring 28. By the downward movement, contact hooks 27A and 27B also downwardly slide on fixed contacts 24A and 24B, respectively, and contact hook 27B leaves from fixed contact 24B. At this moment, the electrical connections between fixed contacts 24A and 24B are broken (i.e., the fixed contacts are in the OFF-state). The signal indicating the OFF-state between contacts 24A and 24B is sent to the electronic circuit of the car, so that each component carries out an operation that should be done in the OFF-state, namely turning OFF the room light, enabling the automatic door lock system, a burglar alarm system, etc.
When the door gets opened, the edge of the door leaves operation head 22A, and accordingly, operation component 22 urged by coil spring 28 moves upwardly. The upward movement brings movable piece 27 up, so that the contact hooks of movable piece 27 make contact with corresponding fixed contacts, i.e., the contacts are in the ON-state, as shown in FIG. 7. The signal thus indicating the ON-state is sent to the electronic circuit of the car, so that the room light is turned ON, and other related components carry out each predetermined operation. Such a vehicle switch having the structure and behavior as described above is disclosed, for example, in Japanese Patent Application Non-Examined Publication No. 2003-132761.
In the conventional vehicle switch described above, the ON/OFF-states of the electrical connections of fixed contacts 24A and 24B are established by the sliding movement of movable piece 27. As contact hooks 27A, 27B are repeatedly rubbed against fixed contacts 24A, 24B over and over again, metallic abrasion powders of contact hooks 27A, 27B and fixed contacts 24A, 24B tend to accumulate between fixed contacts 24A and 24B. Besides, the distance between fixed contacts 24A and 24B is short and the surface is flat. If substrate 24 becomes wet as water accidentally comes into case 21, the structure cannot maintain satisfactory insulation characteristics between fixed contacts 24A and 24B.